Leetcode 707 Design Linked List

Question

Design your implementation of the linked list. You can choose to use a singly or doubly linked list.
A node in a singly linked list should have two attributes: val and next. val is the value of the current node, and next is a pointer/reference to the next node.
If you want to use the doubly linked list, you will need one more attribute prev to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.

Implement the MyLinkedList class:

• MyLinkedList() Initializes the MyLinkedList object.

• int get(int index) Get the value of the index ^th node in the linked list. If the index is invalid, return -1.

• void addAtHead(int val) Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.

• void addAtTail(int val) Append a node of value val as the last element of the linked list.

• void addAtIndex(int index, int val) Add a node of value val before the index<sup>th</sup> node in the linked list. If index equals the length of the linked list, the node will be appended to the end of the linked list. If index is greater than the length, the node will not be inserted.

• void deleteAtIndex(int index) Delete the index^th node in the linked list, if the index is valid.

Example 1:

Input
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"]
[[], [1], [3], [1, 2], [1], [1], [1]]
Output
[null, null, null, null, 2, null, 3]

Explanation
MyLinkedList myLinkedList = new MyLinkedList();
myLinkedList.addAtHead(1);
myLinkedList.addAtTail(3);
myLinkedList.addAtIndex(1, 2);    // linked list becomes 1->2->3
myLinkedList.get(1);              // return 2
myLinkedList.deleteAtIndex(1);    // now the linked list is 1->3
myLinkedList.get(1);              // return 3

Constraints:

• 0 <= index, val <= 1000

• Please do not use the built-in LinkedList library.

• At most 2000 calls will be made to get, addAtHead, addAtTail, addAtIndex and deleteAtIndex.

If you are not familar with linked list, please read the previous article:

Singly Linked list solution

class ListNode {
    constructor(val, next = null) {
        this.val = val;
        this.next = next;
    }
}

var MyLinkedList = function () {
    this.head = null;
    this.tail = null;
    this.size = 0;
};

/**
 * @param {number} index
 * @return {number}
 */
MyLinkedList.prototype.get = function (index) {
  if (index < 0 || index >= this.size) return -1;
  let node = this.getNode(index);

  return node ? node.val : -1
};

/**
 * @param {number} val
 * @return {void}
 */
MyLinkedList.prototype.addAtHead = function (val) {
    let node = new ListNode(val, this.head);
    this.head = node;
    if (!this.tail) {
        this.tail = node;
    }
    this.size++;
};

/**
 * @param {number} val
 * @return {void}
 */
MyLinkedList.prototype.addAtTail = function (val) {
    let newNode = new ListNode(val);
    if (!this.head) {
        this.head = newNode;
        this.tail = newNode;
    }
    this.tail.next = newNode;
    this.tail = newNode;
    this.size++;
};

/**
 * @param {number} index
 * @param {number} val
 * @return {void}
 */
MyLinkedList.prototype.addAtIndex = function (index, val) {
     if (index < 0 || index > this.size) return;
  if (index === 0) {
    this.addAtHead(val);
    return;
  }
  if (index === this.size) {
    this.addAtTail(val); 
    return;
}
  let preNode = this.getNode(index - 1);
  if (!preNode) return; 
  let newNode = new ListNode(val);
  newNode.next = preNode.next;
  preNode.next = newNode;
  this.size++;
};

/**
 * @param {number} index
 * @return {void}
 */
MyLinkedList.prototype.deleteAtIndex = function (index) {
    if (index < 0 || index >= this.size) return;
    if (index === 0) {
        this.head = this.head.next;
        if (index === this.size - 1) {
            this.tail = this.head;
        }
        this.size--;
        return;
    }
    let node = this.getNode(index - 1);
    node.next = node.next.next;
    if (index === this.size - 1) {
        this.tail = node;
    }
    this.size--;
};

MyLinkedList.prototype.getNode = function (index) {
    if (index < 0 || index >= this.size) return null;
    let curr = this.head;
    while (index-- > 0) {
        curr = curr.next;
    }
    return curr;
};

/**
 * Your MyLinkedList object will be instantiated and called as such:
 * var obj = new MyLinkedList()
 * var param_1 = obj.get(index)
 * obj.addAtHead(val)
 * obj.addAtTail(val)
 * obj.addAtIndex(index,val)
 * obj.deleteAtIndex(index)
 */